The present invention relates to a transducer using a thin film of piezoelectric material and in particular to a transducer using a lead titanate (PbTiO.sub.3) thin film having an excellent piezoelectric property.
Lead titanate PbTiO.sub.3 has a large crystal lattice anisotropy and a large spontaneous polarization Ps in the ferroelectric phase (in the tetragonal system). It also has a very large piezoelectricity and a very large pyroelectricity in the polarization axis (c-axis). A piezoelectric transducer using the lead titanate is disclosed in co-pending U.S. patent application Ser. No. 824,728 filed on Jan. 31, 1986 and entitled "Piezoelectric Transducer and process for its production". When a thin film is formed by applying the sputtering method or the like to lead titanate PbTiO.sub.3, a polycrystalline film having random crystal axes is generated. Accordingly the property of lead titanate PbTiO that the piezoelectricity in the c-axis direction is large is not sufficiently achieved.
On the other hand, it is known to make a lead titanate thin film epitaxially grow on a single crystal substrate made of MgO, for example. In order to use the PbTiO.sub.3 thin film as a piezoelectric device or a pyroelectric device, however, it is necessary to dispose an electrode on the underlayer. Therefore, it was attempted to dispose at first an electrode film by using a single crystal substrate and dispose a piezoelectric film thereon.
For example a (100)-oriented platinum thin film is formed on a MgO single crystal substrate, and a c-axis oriented PbTiO.sub.3 thin film is formed on this electrode as described in Japanese patent laid-open application JP-A-59-123285 (1984) or Journal of Applied Physics Vol. 60, No. 1, Pages 361-367 (1986). When this method is used, a c-axis oriented PbTiO.sub.3 thin film is obtained. Since the Pt film is disposed as the intermediate layer, however, the property deterioration is inevitable as compared with the case where the PbTiO.sub.3 thin film is formed directly on the single crystal substrate.